The sizes I have are .060"/1.5 mm ( 10 pcs./pack )- great for small fuel
lines; .080"/2.0 mm ( 10 pcs./pack )- good for oil lines; .100"/2.5 mm ( 5
pcs./pack )- good for larger oil lines, and .125"/3.2 mm ( 5 pcs./pack )- best
for larger scales like 1/16.

Since they are white styrene, it's really easy to get the rounded end of
the fitting by simply filing or sanding the edge. It's also easy to drill a
hole for a locating pin. Then, just cut them to the length you need. I use
Sharpie red & blue markers for the "anodizing". I also use small diameter
wire to form the "elbows".

Here are some engines of some models I've used the Plastruct hex rods
on...........